Robust Receiver Design for Equatorial Regions During Solar Maximum

M. Najmafshar, F. Ghafoori, S. Skone

Abstract:	Random and rapid fluctuations in the amplitude and phase of a trans-ionospheric radio signal, caused by electron density irregularities in the ionosphere, are known as scintillation. GNSS signals are vulnerable to these phenomena and ionospheric scintillations can degrade performance of GNSS receivers. Amplitude scintillation causes the signal-to-noise ratio to drop below the receiver threshold; when this depth of fading exceeds the fade margin of the receiver, signal loss and cycle slips may occur. Phase scintillation induces rapid phase shifts which may exceed the phase lock loop bandwidth. Both amplitude and phase scintillation increase the root mean square (RMS) of phase tracking error at the output of the phase lock loop. Amplitude scintillation is characterized by S4, which is the standard deviation of the received signal power normalized by its mean value, and phase scintillation is measured in terms of standard deviation of the detrended carrier phase. In previous periods of solar maximum, more than 20 percent of L1 phase observations were corrupt during the active equatorial scintillation months (October and March) in Brazil. Many studies in recent years have relied on simulation to determine expected scintillation impact on new GNSS signals and applications. For example, efforts have been made to characterize receiver performance – in terms of cycle slips, mean time between cycle slips and signal-to-noise ratio – in anticipation of the current solar maximum. Optimal receiver designs have been proposed but with only limited data available for validation. In Fall 2012 some of the most severe scintillation events of the current solar cycle were observed in Brazil – with an unprecedented opportunity to quantify and evaluate GNSS receiver performance for modernized GPS and user applications. In this study, we present new analysis of receiver design considerations for equatorial scintillation – for a variety of receiver designs and standalone user applications. We exploit GNSS data collected in 2012 at IBGE (Brazilian Institute of Geography and Statistics) in Rio de Janeiro using a University of Calgary Leapfrog front- end. IF samples from scintillation events are processed using a software receiver developed at University of Calgary (GSNRx). The software receiver has capabilities for simulating various oscillator characteristics, correlators, etc. such that low-cost and survey-grade receiver designs are evaluated. Scintillation levels are quantified by amplitude and phase scintillation parameters estimated from the In-Phase (I) and Quadra-Phase (Q) components and carrier phase information derived by the software receiver. Properties including correlation of scintillation effects between multi-frequency observations are quantified for the equatorial ionosphere – and are used in design and implementation of adaptive tracking loop methods. Optimal receiver design parameters and mitigation methods are proposed for the various receiver models. Results are validated using the real data sets for challenged user applications.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3255 - 3262
Cite this article:	Najmafshar, M., Ghafoori, F., Skone, S., "Robust Receiver Design for Equatorial Regions During Solar Maximum," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3255-3262.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In